During operation of an internal combustion engine, it is desirable to control the formation and emission of certain gases, such as the oxides of nitrogen (NO.sub.x). One method of achieving this result is the use of exhaust gas recirculation (EGR) which is a process whereby exhaust gases are selectively routed from the exhaust manifold or manifolds to the intake manifold of the internal combustion engine. The use of EGR reduces the amount of NO.sub.x produced during operation of the internal combustion engine. In particular, NOx is produced when nitrogen and oxygen are combined at high temperatures associated with combustion. The presence of chemically inert gases, such as those gases found in the exhaust of the engine, inhibits nitrogen atoms from bonding with oxygen atoms thereby reducing NO.sub.x production.
A drawback with using EGR on a turbocharged diesel engine is that EGR cannot be used under conditions where the average pressure of air in the intake manifold is greater than the average pressure of exhaust gases in the exhaust manifold. Using EGR under these conditions would result in a net flow of air from the intake manifold to the exhaust manifold, rather than a net flow of exhaust gases from the exhaust manifold to the intake manifold.
One solution to this problem is to increase the average pressure of exhaust gases in the exhaust manifold. Increasing the average pressure in the exhaust manifold is easily achieved by reducing the size of the turbocharger housing or by routing the exhaust gases through an orifice prior to entering the turbocharger housing. However, increasing the average pressure in the exhaust manifold has a drawback in that the engine must expend more energy to advance the exhaust gases from each cylinder to the exhaust manifold.
For applications involving earthmoving equipment and large trucks, the turbocharged diesel engine is configured for rapid response, e.g. the engine must respond rapidly to changing load conditions. To achieve rapid response, small volume exhaust manifolds are connected to specific exhaust ports in order to preserve the pressure of each pulse of exhaust gases that is created when an exhaust valve is opened. The pulses of exhaust gases are directed to the turbocharger's turbine disk which accelerates the turbine disk at a higher rate than is possible when using a large volume exhaust manifold. The turbine disk drives a shaft which accelerates the turbocharger's compressor at the same rate as the turbine disk. The higher compressor acceleration rate enables the turbocharger to compress a greater amount of intake air. The greater amount of air introduced into the cylinders allows more fuel to be burned which increases the engine's power output. The increased power output allows the engine to respond more rapidly to changing load conditions. Furthermore, as turbocharger efficiencies improve, the turbocharger compresses more air into the intake manifold, the average pressure of the air in the intake manifold can become greater than the average pressure of exhaust gases in the exhaust manifold thereby preventing the use of EGR systems which have heretofore been designed. However, the instantaneous pressure of each pulse of exhaust gases in the exhaust manifold during certain operating conditions is greater than the instantaneous pressure of the compressed air in the intake manifold.
In order to utilize the pressure pulses of exhaust gases for EGR purposes, an EGR valve should preferably be configured to open when each of the high pressure pulses is present in the exhaust manifold, and to close when the instantaneous pressure in the intake manifold is greater than the instantaneous pressure in the exhaust manifold (i.e. between pulses of exhaust gases). Thus, the EGR valve could advance exhaust gases from the exhaust manifold to the intake manifold when the average pressure of exhaust gases in the exhaust manifold is less than the pressure of air in the intake manifold without increasing the average pressure of exhaust gases in the exhaust manifold.
What is needed therefore is an apparatus and method for advancing EGR gases which overcome one or more of the above-mentioned drawbacks.